1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method for the semiconductor device, and particularly, relates to a semiconductor device having an active region provided by ion implantation and a manufacturing method for the semiconductor device.
2. Description of the Related Art
Control of the impurity distribution in a semiconductor layer is extremely important. For example, in a minute metal-oxide-semiconductor (MOS) transistor fabricated on a silicon (Si) semiconductor substrate, an impurity diffusion layer is required to be formed to have a shallow and abrupt impurity profile to achieve a high drive current, and to suppress a short channel effect.
For example, in source/drain extension regions of a MOS transistor, a shallow pn junction must be formed with a thickness of or less than twenty nm from a surface of a semiconductor substrate. In order to form a shallow pn junction, a shallow impurity doped region is required. In the formation of a shallow impurity doped region, ions of an impurity are implanted into a semiconductor substrate at low acceleration energy and a low dose. The impurities implanted into the semiconductor substrate are activated by annealing so as to form a shallow impurity diffusion region.
For example, the diffusion coefficients of p-type impurities such as boron (B), and n-type impurities such as phosphorus (P) or arsenic (As) in the crystal of the Si semiconductor substrate are large. Impurities diffuse out to both the interior and exterior of a semiconductor substrate due to the high temperature of activation annealing, such as rapid thermal annealing (RTA). Therefore, it is difficult to form a shallow impurity diffusion region with a high concentration of impurities in a semiconductor substrate. On the other hand, if activation annealing temperature is decreased in order to suppress diffusion of impurities, a high concentration of impurities may not be activated.
A method for co-implanting ions of nitrogen (N) or molecular nitrogen (N2), and B ions has been suggested as a way of suppressing the diffusion of impurities (refer to Japanese Patent Gazette No. 3442154). However, there is a concern that accelerated diffusion of B ions will occur due to point defects generated by the implantation of the N+ and N2+. Therefore, it is difficult to form a shallow impurity diffusion region having low resistance and a high concentration of activated impurities.